A wireless local area network (WLAN) in infrastructure basic service set (BSS) mode has an access point (AP) for the BSS and one or more stations (STAs) associated with the AP. The AP typically has access or interface to a distribution system (DS) or another type of wired or wireless network that carries traffic in and out of the BSS. Traffic to STAs that originates from outside the BSS arrives through the AP and is delivered to the STAs. Traffic originating from STAs to destinations outside the BSS is sent to the AP to be delivered to the respective destinations.
Traffic between STAs within the BSS may also be sent through the AP where the source STA sends traffic to the AP and the AP delivers the traffic to the destination STA. Such traffic between STAs within a BSS is really peer-to-peer traffic. Such peer-to-peer traffic may also be sent directly between the source and destination STAs with a direct link setup (DLS) using an IEEE 802.11e DLS or an IEEE 802.11z tunneled DLS (TDLS). A WLAN in independent BSS mode has no AP, and the STAs communicate directly with each other.
A network allocation vector (NAV) protection mechanism is used at the medium access control (MAC) layer to protect packet transmissions on the wireless medium. The NAV is an indicator maintained by each device (i.e., the STA or the AP) of time periods when transmission onto the wireless medium will not be initiated by the device. Each frame transmitted in the BSS contains a duration field that is set to a time period corresponding to the transmission of the frame and any subsequent frames, along with interframe spaces as required by the frame exchange sequences defined in the MAC layer protocol. A device that receives a valid frame not addressed to it updates its NAV using the information in the duration field of the received frame if the update results in a new NAV value that is greater than the current NAV value.
In a BSS, packet collisions may result because of hidden node problems. To mitigate this problem, a ready to send (RTS) and clear to send (CTS) frame exchange may be used to set the NAV. To reserve the medium, a device sends an RTS frame addressed to a recipient device as the first frame of a frame exchange sequence. The recipient device responds with a CTS frame addressed to the device that transmitted the RTS frame. In this way, the NAV is set for all other STAs in the neighborhoods of both devices to support the frame exchange sequence.
Another protection mechanism that involves less overhead, but is not as robust, is transmission of a “CTS-to-self” frame before a transmission requiring protection. With this protection mechanism, a device first transmits a CTS frame addressed to itself with a duration value that protects the subsequent transmission.
Devices may be assigned to groups with a group identifier (referred to hereinafter as group ID) using management frames for radio resource management functions. The group ID and associated group information is indicated in the physical (PHY) or MAC portion of a frame. Methods are known for assigning a group ID with associated group parameters to devices using management frames.
WLANs with very high throughput (VHT) of greater than 100 Mbps on top of the MAC layer are being designed. To enhance system performance, VHT WLANs may include features such as: power saving, MU-MIMO, or orthogonal frequency division multiple access (OFDMA). These features may use group transmissions or group frame exchanges, in which more than two devices are involved.
In a MU-MIMO or OFDMA scenario, a given device communicates with more than one STA simultaneously, resulting in multiple simultaneous communication links. With MU-MIMO, the simultaneous communications occur on the same frequency or frequencies. With OFDMA, the simultaneous communications occur on different allocated sub-carrier frequencies. In the uplink (UL) direction (to the device), there is more than one transmitting device and one receiving device. In the downlink (DL) direction (from the device), there is one transmitting device and more than one receiving device.
Because more than two devices are involved in group transmissions or group frame exchanges, the existing protection mechanisms of RTS and CTS frame exchanges (which are designed for only two devices) will not work properly. Similarly, frame response mechanisms such as acknowledgement (ACK) frames and block ACK frames (which are designed for only two devices) will not work properly for group transmissions or group frame exchanges.
For group transmissions or group frame exchanges, the group ID concept described above may be used to provide a signaling protection mechanism, a frame response mechanism, and a sounding mechanism.